The present invention relates to an improvement in thin layer chromatography plates containing concentrating zones.
A series of carrier materials are commercially available, preferably glass plates or also synthetic resin or aluminum foil plates, which are coated with layers suitable for chromatography, especially for thin layer chromatography (TLC), e.g., layers of silica gel. It is also already known to provide a low or non-adsorptive layer of kieselguhr adjacent to and forward of the chromatographically active silica gel layers. Such a layer is termed a concentrating zone.
Because of the differing adsorption properties of the two sorption agents, such as kieselguhr and silica gel, on 200 .mu.common substrate, it is possible to exactly evaluate chromatograms even when samples are not uniformly applied.
In such known concentrating zone-containing TLC plates, the test sample is applied in the concentrating zone. When the eluent is thereafter applied, the entire sample moves rapidly through the practically inactive layer of the concentrating zone up to its very narrow border with the chromatographic zone. At this junction region, all components of the test sample are greatly retarded due to the adsorptive properties of the chromatography layer such as silica gel resulting in a collision-like deacceleration of all components in the test sample, As a result, irrespective of the broadness of the original pattern of the test sample as applied in the concentrating zone, the pattern becomes sharply defined when it enters the chromatography zone.
Whereas for the chromatography layer, the proven silica gel layers are preferably used, hitherto kieselguhr has been used for the inactive concentrating zone. Because of its activity, normal silica gel is not suitable for this purpose. However, the known TLC preparations having such a kieselguhr layer possess considerable deficiencies which result from the properties of the kieselguhr. As a natural product, the quality and properties of the kieselguhr are dependent upon the source from which it is obtained. In addition, very laborious methods of purification are required in order to obtain a material useful for this purpose. Coloring components present in the kieselguhr must be removed; however, very frequently it is not possible to eliminate inorganic salts or traces of heavy metals remaining in the kieselguhr, which disturb the chromatography.